As a tank, if a DPS insists on attacking the wrong targets (I mark everything), they get to deal with it. First time I will ask them to follow marks, and normally they do after that...but those that continue to attack the wrong mark get to play tank.

Its harder to do that as the heal with a random tank, since sometimes tanks just mark just to mark and don't actually care what the DPS does...but if you and the tank are on the same page you can do that